Purple Pole-dancer

The Violet-backed Starling (Cinnirycinclus leucogaster) is a member of the highly successful and widely distributed Starling family. It is common over much of sub-Saharan Africa in moist savanna, woodland and riverine forest and is regarded as a breeding migrant in most of South Africa where it ranges southwards in summer as far as the northern reaches of the Eastern Cape. It feeds mainly on fruit and insects. While naturally gregarious they seldom assemble in large flocks or roost communally. They are monogamous and nest in tree cavities. Where suitable natural cavities are absent they are known to make use of hollow fence posts. Sightings in the Durban area are relatively rare and inevitably engender excitement among birders. In October 2017 we were delighted to discover a pair intent on nesting in a hollow fence post on the border between our property and Krantzkloof Nature Reserve. It provided a good opportunity for observation and photography.

Perhaps the most outstanding feature of this species is the brilliant iridescence of the mature male plumage. The female, in contrast is somewhat drab. The male colouration has been variously described as “amethyst”, “plum-coloured” and “purple”. A precise description is difficult since the hues are not produced by a fixed pigment but rather through the “magic” of light diffraction. Many bird species have micro-structures in their feathers which enable reflective iridescence of specific colours. In some species this capacity has been enhanced to such an extent that they are able to use body position and manoeuvrable feathers to send directed reflective signals. Hugh Chittenden (African Birdlife, November/December 2017, www.birdlife.org.za) provides a superbly illustrated account of this phenomenon in two African species that he regards as outstanding masters of this behaviour (African Emerald Cuckoo and Violet-backed Starling).

As would be expected for breeding migrants, no time was wasted in getting down to business. The full procedure (nest refurbishment to fledging) was completed in about 6 weeks. The pair were first observed on 20 October gathering and nesting material. This consisted at first of coarse dried plant material, followed later by fresh foliage. Both partners were involved. Fresh foliage was added at intervals throughout the nesting period leading to speculation that it may have served a sanitary purpose. Cavity nests are prone to infestation by pests and cavity nesters are known to select specific plant material with “fumigation” properties.

Nest hygiene is clearly a priority in cavity nesters and our pair displayed due diligence in this regard. Faecal sacs were regularly dumped in differing directions about 20 metres from the nest. This practice is thought to also play a role in predator avoidance by reducing and confusing scent trails.

While probably the least raucous of local Starlings this species is, nevertheless, highly communicative. We were often aware of low calls between the pair when they were close to the nest (in an adjacent Protea roupelliae) and busy with food delivery, faecal sac removal or nest maintenance. Given that the birds would be most vulnerable to predators while perched on the pole-top it is tempting to suggest that these calls served to signal intentions so that entries and exits could be better coordinated and more rapid.

Feeding activities were decidedly frenetic. During incubation the male took the leading role. Thereafter, both partners were diligent from sunrise to sunset and made repeated short forays (about 5 minutes). There appeared to be no shortage of suitable food items in the immediate vicinity. The majority of the food items were insects. In the latter stages a preference was shown for fruits of the Coastal Red Beech (Protorus longifolia). There was a clear correlation between food selected and food availability. So, when termite alates were emerging these were delivered in abundance. The following images provide insight into the range of food items that we observed.

These images give some idea of colour variation in breeding male Violet-backed Starlings. This can range from rose pink, through violet to dark bluish purple and black. While the nature of ambient light is a primary factor in generating iridescent displays, posturing and realignment of feather angles allows individual males to tweak and focus the output to enhance communication. The males can effectively morph rapidly from being inconspicuous (dark colouration and hunched to hide the prominent white belly) to aggressively prominent (belly exposed and colour flashes).

Their nuptial display typically includes “wing-flagging” by the males (rapid raising and lowering of the wings) which is often accompanied by iridescent dorsal flashes. The images below have captured this behaviour. On both occasions the male is simultaneously offering food. Perhaps signaling that he is not only a fine specimen but also a good provider.

In contrast, the females are less exuberant in their visual communication. However on one occasion we witnessed an extraordinary display. It happened at a time when the pair had assumed shared feeding duty. The female was perched on the nest when the male returned with a particularly tasty looking snack. She immediately crouched in a posture that would seem to reflect great interest, excitement and/or aggression. In a flash the grub changed beaks and both birds flew off. It happened too fast to judge if it was an amicable exchange or a sneaky snatch. We do know that the nestlings lost out. Note that the female’s iris is momentarily expanded to reveal a yellow flash. This phenomenon, known as “iris signaling”, is fairly common among bird species where it is used to convey a variety of emotions and intents. Anthropomorphic interpretation is often difficult. My interpretation of this behavior is that the expanded iris was directed at drawing attention (“here I am, look at me”) while the low angled posture and upturned bill was shouting “I am submissive and need that grub right now”.

Forty three days after we first noticed the birds collecting nesting material two fledglings emerged from the fence post (a difficult and constrained one-metre vertical journey). We had purposely avoided close internal inspection of the nest so did not know how many to expect. Emergence was quite prolonged and involved physical assistance and prodding plus coaxing with food. By sunset only one was out and it flew immediately to a nearby Protea roupelliae. At sunrise the following day the second fledgling was coaxed out with food. All four birds remained in the vicinity of the nest for about 24 hours and departed on 2 December. The close resemblance of the fledglings to the adult female and their immediate mobility was quite remarkable.

Tarboton, W, (2001). A guide to the nests and eggs of Southern African Birds. Struik.

About the author

Tim and Helen McClurg are long term members of Kloof Conservancy and Birdlife South Africa. They lived on the edge of Krantzkloof Nature Reserve for many years but have recently relocated to Renishaw on the KZN South Coast. Tim is a semi-retired marine scientist.

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The Leopard's Echo is Kloof Conservancy's bi-annual magazine. We feature articles on a variety of nature-related topics that celebrate our wonderful biodiversity.

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